It is often desired to establish a flow of gas. For example, a flow of gas may be injected into a liquid for one or more of several reasons. A reactive gas may be injected into a liquid to react with one or more components of the liquid, such as, for example, the injection of oxygen into molten iron to react with carbon within the molten iron to decarburize the iron and to provide heat to the molten iron. Oxygen may be injected into other molten metals such as copper, lead and zinc for smelting or refining purposes or into an aqueous liquid or hydrocarbon liquid to carry out an oxidation reaction. A non-oxidizing gas, such as an inert gas, may be injected into a liquid to stir the liquid in order to promote, for example, better temperature distribution or better component distribution throughout the liquid.
Often the liquid is contained in a vessel such as a reactor or a melting vessel wherein the liquid forms a pool within the vessel conforming to the bottom and some length of the sidewalls of the vessel, and having a top surface. When injecting gas into the liquid pool, it is desirable to have as much gas as possible flow into the liquid to carry out the intent of the gas injection. Accordingly gas is injected from a gas injection device into the liquid below the surface of the liquid. If the nozzle for a normal gas jet were spaced some distance above the liquid surface, then much of the gas impinging on the surface will be deflected at the surface of the liquid and will not enter the liquid pool. Moreover, such action causes splashing of the liquid which can result in loss of material and in operating problems.
Submerged injection of gas into liquid using bottom or side wall mounted gas injection devices, while very effective, has operational problems when the liquid is a corrosive liquid or is at a very high temperature, as these conditions can cause rapid deterioration of the gas injection device and localized wear of the vessel lining resulting in both the need for sophisticated external cooling systems and in frequent maintenance shut-downs and high operating costs. One expedient is to bring the tip or nozzle of the gas injection device close to the surface of the liquid pool while avoiding contact with the liquid surface and to inject the gas from the gas injection device at a high velocity so that a significant portion of the gas passes into the liquid. However, this expediency is still not satisfactory because the proximity of the tip of the gas injection device to the liquid surface may still result in significant damage to this equipment. Moreover, in cases where the surface of the liquid is not stationary, the nozzle would have to be constantly moved to account for the moving surface so that the gas injection would occur at the desired location and the required distance between the lance tip and bath surface would be maintained. For electric arc furnaces, this requires complicated hydraulically driven lance manipulators which are expensive and require extensive maintenance.
Another expedient is to use a pipe which is introduced through the surface of the liquid pool. For example, non-water cooled pipes are often used to inject oxygen into the molten steel bath in an electric arc furnace. However, this expediency is also not satisfactory because the rapid wear of pipe requires complicated hydraulically driven pipe manipulators as well as pipe feed equipment to compensate for the rapid wear rate of the pipe. Moreover, the loss of pipe, which must be continuously replaced, is expensive.
These problems can be solved if a coherent jet can be established. A coherent gas jet retains its diameter and velocity, after ejection from a nozzle, far longer than does a normal gas jet. With a coherent jet, the injector tip may be positioned significantly further from the liquid surface while still enabling virtually all of the gas within the coherent gas jet to penetrate the liquid surface.
It is known that a coherent jet of an oxidizing gas can be established by surrounding the jet of oxidizing gas upon its ejection from a nozzle with a flame envelope formed by an annular stream of fuel around the oxidizing gas jet and a stream of oxidant annular to fuel stream. The fuel and oxidant combust to form the flame envelope which flows coaxially with the oxidizing gas stream and maintains it coherent for a long distance after ejection from the nozzle. However, this flame envelope arrangement does not work well if the gas is an inert gas. In such situations the velocity of the gas jet is quickly reduced and the coherency of the inert gas jet deteriorates rapidly. This is a particular problem where it is desired to switch from an oxidizing to an inert gas as this requires alteration of the gas lance ejection system.
Accordingly, it is an object of this invention to provide a method for maintaining the velocity and the coherency of a gas jet irrespective of whether the gas jet is an oxidizing or an inert gas jet.
It is another object of this invention to provide a method for maintaining the velocity and the coherency of a gas jet while enabling the composition of the gas jet to be changed.